1. Field of the Invention
Our invention lies in the field of data transfer and more specifically in the field of methods and apparatus for comparing images and recording selected matter as perceived from compared images on an output record sheet.
2. Description of the Prior Art
A. Camera Lucidas
Several instruments employing semireflective optics to combine an image of a tracing manuscript with an image of a photograph are known, the respective distances to the photograph and the manuscript being variable to match their scales for tracing purposes. Such instruments are also known with introducible magnifying and minifying lenses to help accommodate scale matching problems.
Ambrose, A Radar Image Correlation Viewer, 33 Photogrammetric Engineering, 211-214, (Feb. 1967), describes a semireflective binocular bar prism in fixed equidistant orientation to a manuscript easel and a rear projection screen, mechanisms being provided in a somewhat elaborate projection system for image rotation, autofocusing variable magnification to match the manuscript scale, and for anamorphic (one-directional stretch) magnification to compensate for such image distortions as may have been induced by camera tilt, variable topography and other causes.
B. Compound Microscopes for Film Viewing
Compound microscope optical systems have been employed for viewing photographic films. Sophisticated instrumentation is known which may include two or more compound optical systems having image rotators, zoom variable magnification systems and anamorphic image stretchers, the images from the various optical systems being directable to separate eyepieces for stereoviewing, or combinable for comparison of photographically recorded features.
C. Camera Lucidas in Compound Microscopes
The microscope art has for several decades included external camera lucida attachments which comprise a semireflective member placed diagonally across the image path emerging from a microscope eyepiece, and a mirror aligned to deflect an image of a tracing sketch onto the semireflective member for relay to an observer's eye when sketching microscopic images.
A difficulty with most camera lucida devices is that the images to be combined have different conjugates to the semireflective member, thereby forcing the viewing eye to try to focus at both distances simultaneously, which quickly induces eyestrain. Another operator fatigue problem arises from prolonged body contortion required for parallax-free viewing through a semireflective member whose position may have been dictated by the need to overcome photographic distortions due to tilts in the taking camera, or to other causes. Ambrose' Correlation Viewer, above described, was free of these problems, but its use of a projection system necessitated losses of photographic image resolution inherent in projections upon a screen.